In a bidirectional drive tape cartridge of the type shown in U.S. Pat. No. 3,692,255 in which the tape moves at high speeds between two reels and is subjected to high accelerations when the tape direction is reversed, it is important to minimize tape tension variations at the transducer head. Otherwise tape to head contact may be lost and data compromised.
One approach to reducing tension variations is shown in U.S. Pat. No. 4,221,348 which utilizes first and second tape wrap pins each mounted along the tape path between a reel and an associated tape guide. The tape wrap pins function to maintain the wrap angles around the guides more constant as the radius of the tape disposed on the reels varies between a minimum and a maximum. Despite the incorporation of the tape wrap pins, the tension still exhibits some variation between the beginning of tape (BOT) and the end of tape (EOT) and vice versa. Typically, tension increases from BOT to EOT by approximately 20%. Tests have revealed that although the pin upstream from the head has the most influence on the tension, in fact both pins contribute to the tension variations.
In a test using only a pin on the upstream side of the head, tension variations were reduced substantially as compared to the two pin case.